1. Field of the Invention
The invention relates generally to lighting devices and lighting fixtures and, more particularly, to a lighting device which activates a light source being a solid-state light emitting element, and a lighting fixture comprising the same.
2. Description of the Related Art
Recently, a lighting device and a lighting fixture have rapidly become widely used, which adopts, as a light source, a solid-state light emitting element such as a light-emitting diode or an organic electroluminescence (EL) element, as substitute for an incandescent lamp and a fluorescent lamp. For example, Japanese Patent Application Laid-Open No. 2011-108671 discloses a lighting device (an LED dimming device) which adopts, as a light source, a light-emitting diode (LED) and adjusts (dims) amount of light outputted from the LED based on a dimming signal provided by a dimmer.
Here, as a dimming method of LED, there are a dimming method in which magnitude of current continuously flowing to an LED is changed (hereinafter, called DC (Direct Current) Dimming Method), a dimming method in which a ratio of a conducting period (a duty cycle) is changed by periodically switching the current flowing to an LED on and off (hereinafter, called Burst Dimming Method), and the like. Then, as the conventional lighting device described in the above-mentioned document, there is also a case in which when the dimming level is relatively high (bright), the DC Dimming Method is adopted, and when the dimming level is relatively low (dark), the Burst Dimming Method is adopted.
Incidentally, as the conventional lighting device described in the above-mentioned document, the lighting device and lighting fixture adopting the DC Dimming Method has a problem that when decreasing current continuously flowing to an LED, the emission color of the LED changes in response to magnitude of the current.
Generally, a switching power circuit is used in a lighting circuit that activates an LED. As the dimming level in the Burst Dimming Method is reduced, the conducting period during which the switching power circuit performs the switching operation shortens, thereby increasing variation in the number of the switching operation performed by the switching power circuit within the conducting period. Therefore, there is a problem that the lower the dimming level is, the more variation in amount of light increases.